Video transmission systems which employ some form of angle modulation (e.g., frequency or phase modulation) of a carrier wave to convey the video information are well known. Examples include Video Tape Recorders (VTR's) and satellite transmission systems of the type employing FM transponders for relaying the video signal.
It is known that video FM transmission systems are subject to a form of noise known as "triangular" noise. Triangular noise is characterized by noise power which increases with frequency as compared with Gaussian or White noise wherein the noise power is constant with frequency or so-called "1/F" where the noise power increases with decreasing frequency.
It is known to use preemphasis of the high-frequency portions of a video signal before FM modulation to amplify those high-frequency portions before transmission over the FM link, followed by a deemphasis to reduce the amplitude of the high-frequency components to the then correct relative value. However, the dynamic range of the FM system must be increased to accommodate the preemphasized signal.
It is known that an improvement in the signal-to-noise ratio (S/N) of the displayed image of a television receiver may be obtained by the method of separating the video signal into high frequency (HF) and low frequency (LF) components, coring the HF component and then adding the non-cored LF component to the cored HF component. Examples of analog circuits which provide noise reduction by coring include U.S. Pat. No. 3,715,477 entitled, Video Signal Noise Limiting Apparatus which issued Feb. 6, 1973, to Olson et al. and U.S. Pat. No. 4,009,334 entitled, Video Noise Reduction Circuit which issued to R. J. Sypula, Feb. 22, 1977. Such circuits completely eliminate noise having amplitudes less than the coring threshold.
Coring is, of course, not limited to analog circuit implementations. An example of a digital coring circuit is provided in the article "Digital Techniques for Reducing Television Noise" by John P. Ross which was published in March, 1978, in the SMPTE Journal, Vol. 87, pp 139-140.